Packaged electrodes for the cathodic protection of metallic underground structures



2,621,154 HODIC PROTECTION STRUCTURES Dec, 9, 1952 R PACKAGED ELECTRODEOF METALLIC Fil B. MEARS S FOR THE CAT UNDERGROUND ed Oct. 25, 19

VENTOR R Means 11v oberi B Patented Dec. 9, 1952 UNITED STATE s PATENTOFFICE JPACKAGEDELECTRODES FOR THE GA- THODIC PROTECTION OF METALLICUNDERGROUND STRUCTURES Application October 25, 1946, Serial No. 705,508

"3 Claims. l

This inventionrelatesto .a novel. electrode or anode package designedfor use :as .a part of an installation designed to protect metallicunderground ,structures, such as pipe lines, oil well casings or parts,structural footings and thelike, against corrosion and corrosiveagentsoragencies. In such installations .a metal electrode, made 'oimetalanodicto the metal of the structure .to be protected, is buried in the earthat a distance from the metallic underground structure and connected.thereto by :a conducting wire or bus thereby forming a galvanic cell,the earth serving ,to complete the circuit. When such installations areproperly made, a steady current flows continuously inthe cell .so formedand offers, as is well known, considerable protection against corrosionto the :buried metallic structure.

The present invention relates to improvements in such installationsbeing primarily directed to the provision of .an-improved electrodeassembly or package of very considerable advantages. The objects,purposes and advantages of the inventionare'best describedwithxreference to the accompanying drawings, .inwhich:

"Fig.1 isa diagrammatic representation, shown in cross-sectionalelevation, of a portion of a typical installation made in accordancewith prior -practice,'to cathodically protect a metallic undergroundstructure;

.Fig.12'iS a view in ,orcssasectional elevation, through-:anelectrodepackage embodying this invention in preferred form;

Fig. 3 is a view ofza cross section through the package shown in :Fig.line 3-3;

.Fig. 4 illustrates, in cross sectional elevation, another electrodepackage embodying the principles of this invention.

Discussion of the conventional installation illustrated in Fig. 1 willserve to illustrate the reasons'for :and theadvantages of the presentinvention. The metallic underground structure to be protected isillustrated by a pipe line In buried in the earth ll. An electrode l3 isburied a distance from the line It and connected thereto by the'wire.l2. Usually a number of electrodes are employed when a buried linearstructure, such-as aiipipe line, is to beprotected, the electrodes beingspaced along the run of the line at 2, taken at the section iii)suitable intervals and connected to the line as illustrated .in thefigure. Only-one electrodeis shown in the illustration. in someinstallations.

a series of single electrodes is connected at intervals along thepipeline. In other installations groups of electrodes may be disposed atintervals along theline, each group being connected tothe line with asinglelead. "The. electrode l3 is installed in ,a hole dug in the earth,the outline of the hole being indicated in'Fig. 1 by the broken line I4.The electrode is positioned in-the hole and then maintained in thisdesired ,positionby tamping or pressingthemixture l5 around it..Thereafter, in usual practice, anearth cap l6"-is placed on top of themixture l5toifill the hole to the earth level IT. "The mixture l5 isprepared at the time of. installation and comprises a carrier or base,often ,formed of earth, with which are mixed chemicals of predeterminednature and quantity. These chemicals have various functions but .areusually considered necessary to promote efficient operation of theelectrode and of the "cell of .which the electrode is apart. Thechemicals, ,the exact nature an'd quantity of which form no partof'thisinvention, often difier according to the compositionlof the metallicelectrode l3, the nature of .the' current desired in the cell and thejudgmentof the person making the installation. In any event, thechemical substances are predetermined as an active element of theinstallation. As above stated, they metal of the ,electrodeis anodic tothe metal of the structure to be protected, andsince such structuresareusuallymade of iron orsteel, it has been common practice to use zincelectrodes. Recent developments in .the utilization of aluminum and,magnesium metals as. electrodes have opened thecommercial utilizationof these metals. Whatever the metal chosen .as

electrode, and the chemicals chosen as the active element of themixtureor fbackfill. surrounding the installed electrode, the practice ofinstallation has been as described, jthe mixture being made, .at thetime each electrode is installed, from materials brought to thefield andthen pressed or tamped around the electrode. Besides requiring an undueamount of time and transportation of chemicals to the field, suchbackfllling operations have reguired constant supervision to makecertain that the backflll mixtures are of proper concentration. This istrue not only at the time the electrodes are installed but also whenreplacement of the electrode is necessary.

These distinct disadvantages of the present installation practices areovercome, the job of installation and replacement simplified andaccuracy of the final result insured by the present invention.

In accordance with this invention a preformed electrode package isprepared which essentially consists of a metallic electrode of desiredcomposition surrounded by a rigid permeable envelope containing thechemical components predetermined as the desired active elements in thefinal installation. Thus electrode and envelope comprise a single unit.In practice this packaged electrode may be transported as such to theplace of installation, dropped, or planted, in a hole dug to receive itand the installation finished by connecting the electrode to thestructure to be protected. Thereby the necessity for preparing a mixturein the field is avoided, accuracy of mixture is assured and the Work ofinstallation considerably lessened. Such electrode packages are, I havefound, as eilicient in operation as the field-assembled installationswhich they replace, and in some instances there have been indicationsthat over extended periods of time the operation of the galvanic cell ofwhich the installed package is a part is more eiiicient.

The preformed electrode package of this invention may take variousshapes and forms. Examples are illustrated in Figs. 2 to 4, inclusive.The package is formed by casting or pressing or otherwise forming on theselected electrode a rigid mass which contains the active chemicalelements. Such a form of package is shown in Figs. 2 and 3, a rigidcement envelope l9 having been cast upon the metallic electrode it. Inthis case the package has also been provided with a connecting lead 20,the point of attachment of the lead to the electrode I8 having beencovered with a protective cap 2!, here made of asphalt, to prevent unduecorrosion at this point. In the form shown in Fig. 2 the rigid envelopel9 entirely surrounds the electrode but such construction is notnecessary and only a substantial portion of the electrode surface needbe covered. Thus in the form shown in Fig. 4 the rigid permeable mass 23only covers a portion of the electrode 22, the wire lead 24 and theprotecting cap 25 being again conveniently provided. In these forms therigid mass or envelope I9 or 23 may be formed of cement, plastic,ceramic, some forms of gelatin, or other moldable substance which, whenmolded into contact with the electrode, forms a rigid permeable envelopeor coating.

The term rigid as used herein means that the mass surrounding theelectrode should have sufficient stiffness to be self supporting. Theenvelope or coating must be of such a character as to allow any liquidand chemical to come in contact with the electrode and this property isherein designated as permeability. the surrounding mass will havechannels or pores of a suilicient size to be readily detected and hereinmasses of this nature are regarded as being porous.

The chemicals required in the mass may in many cases, depending on thechemicals desired and the material of which the mass is formed, be mixedwith the mass prior to placing it around the electrode or a neutral massmay be employed and after it is placed on the electrode In most casesthe required chemicals may be placed in its pores by immersion of thearticle in a solution of the chemical, followed by drying, or byfamiliar methods of pressure impregnation or in any other convenientmanner.

Other substances than the required chemicals may be present but theyshould not, of course, destroy the eifect of the chemicals. Also inparticular cases it may be desirable to apply first a coating to theelectrode with a chemical which alters rate of reaction with thesurrounding envelope before molding or casting the said envelope aboutthe electrode.

In any event, the result is an electrode package consisting essentiallyof a metallic electrode at least partially enveloped in a rigidpermeable mass, the mass containing chemical predetermined to be anactive element in the cathodic protection installation of which theunitary package will become a part. While exact compositions form nopart of this invention, some examples thereof will serve to illustratethe invention in its preferred form. For instance, if the packagecontains a zinc or magnesium electrode, the permeable envelope may beformed of a calcium sulphate cement or a Portland cement to whichsulphates have been added, since sulphates are chemicals often chosenfor the back fill mixture when such electrodes are used. If theelectrode be of aluminum and it is desired to use an alkaline backfillmixture of substantial halide content, such as the mixtures proposed byR. H. Brown in his copending application, Serial No. 693,593, filedAugust 28, 1946 (now Patent No. 2,565,544), the envelope element of thepackage may be formed of an alkaline cement in which amounts of halideshave been incorporated. Good results have been obtained with a packageconsisting of n aluminum electrode surrounded by a rigid permeable massmade of cement consisting of a mixture of equal parts of magnesite andsand moistened to a paste consistency, prior to molding, by a saturatedsolution of magnesium chloride.

Cements generally re preferred in the construction of the electrodepackage of this invention because of their inherent chemicalcomposition, their protective qualities, their permeable nature and theease and cheapness of the operation of casting the cement around theelectrode to form a unitary preformed electrode package which may bereadily handled and transported.

The words aluminum, magnesium and zinc are used herein to designate themetallic nature of the electrode and are used in the sense of aluminous,magnesic or zincous metals and are, therefore, not intended to exclude,by implication or otherwise, alloys containing these metals in suchquantities s to make such alloys useful in a cathodic protection system.

Having thus described my invention, I claim:

1. In a cathodic protection system an underground metallic structure,said structure being electrically connected to a separately installedunderground electrode of a metal anodic to the metal of said structure,and said electrode being at least partially enveloped and fixedlycontacted by a rigid cement mass containing chemical predetermined as anactive element in said system, said mass being permeable to liquid.

2. In a cathodic protection system an underground metallic structure,said structure being electrically connected to a separately installedunderground aluminous electrode, said electrode being at least partiallenveloped and fixedly contacted by a rigid cement mass containingchemical predetermined as an active element in said system, said massbeing permeable to liquid.

3. In a cathodic protection system an underground metallic structure,said structure being electrically connected to a separately installedunderground magnesic electrode, said electrode being at least partiallyenveloped and fixedly contacted by a rigid cement mass containingchemical predetermined as an active element in said system, said massbeing permeable to liquid.

ROBERT E. MEARS.

REFERENCES CITED The following references are of record in the file ofthis patent:

6 UNITED STATES PATENTS Number Name Date 609,745 Luxton Aug. 23, 18981,236,693 Ellis Aug. 14, 1917 1,433,017 McKee Oct. 24, 1922 2,495,465Miller Jan. 24, 1959 FOREIGN PATENTS Number Country Date 2,927 GreatBritain of 1884 QTHER REFERENCES Corrosion, vol. 1, No. 2, June 1945,pages 59 thru 62.

1. IN A CATHODIC PROTECTION SYSTEM AN UNDERGROUND METALLIC STRUCTURE, SAID STRUCTURE BEING ELECTRICALLY CONNECTED TO A SEPARATELY INSTALLED UNDERGROUND ELECTRODE OF A METAL ANODIC TO THE METAL OF SAID STRUCTURE, AND SAID ELECTRODE BEING AT LEAST PARTIALLY ENVELOPED AND FIXEDLY CONTACTED BY A RIGID CEMENT MASS CONTAINING CHEMICAL PREDETERMINED AS AN ACTIVE ELEMENT IN SAID SYSTEM, SAID MASS BEING PERMEABLE TO LIQUID. 